Different types of needleless injection devices are described, for instance, in U.S. Pat. Nos. 5,062,830 issued to Dunlap; U.S. Pat. No. 4,790,824 to Morrow et al.; U.S. Pat. No. 4,623,332 to Lindmayer et al.; U.S. Pat. No. 4,421,508 to Cohen; U.S. Pat. No. 4,089,334 to Schwebel et al.; U.S. Pat. No. 3,688,765 to Gasaway; U.S. Pat. No. 3,115,133 to Morando; U.S. Pat. No. 2,816,543 to Venditty et al.; and U.S. Pat. No. 2,754,818 to Scherer. These injectors have been contemplated to administer medication as a fine, high velocity jet, delivered under sufficient pressure to enable the jet to pass through the skin tissue without requiring a hypodermic needle. These injectors typically have a nozzle assembly having an internal chamber for holding medication. The nozzle member has an orifice through which a jet stream of medication is forced out from the chamber typically using a plunger attached to an energy source, most commonly a coil spring, as described for instance in the aforementioned '830, '543 and '818 patents.
Needleless injectors provide a relatively painless and efficient way of administering medication to a percutaneous or subcutaneous tissue zone, for example, and therefore are deemed better suited for such use. For example, persons afflicted with diabetes mellitus need to take one or more daily doses of insulin to maintain an appropriate glycemic balance. When a hypodermic needle is used, due to the natural aversion to piercing oneself with the needle, patient compliance with physician's dosage regimen can be hampered. On the other hand, when a needleless injector is used, since there is no needle, any apprehension of piercing oneself with a needle is substantially eliminated, allowing the patient to better comply with the dosage regimen. Moreover, repeated needle injection to the same tissue area may lead to skin or tissue damage. The needleless injector also affords a further advantage in that the medication is dispersed through a greater volume of subcutaneous tissue than when a bolus injection is introduced through a conventional hypodermic needle.
Further, with the advent of the spread of AIDS, hepatitis and other viral diseases, medical communities have become quite concerned over the possibility of accidental "sticks" involved with use of conventional hypodermic needles and problems associated with disposing the same. Special waste containers or the like thus have been mandated to collect and dispose used needles. The needless injection devices eliminate the problems associated with used needles and thus are better suited for use.
Notwithstanding the advantages obtained with needleless injectors in general, the presently known portable needleless injectors, however, do pose certain shortcomings. These include the inability to provide sufficient and generally substantially constant pressure over the period during which the medication is ejected from the nozzle assembly. Consequently, the medication within the nozzle assembly may not be fully injected to a target zone if the spring force is not sufficiently high throughout the injection period, which can lead to a "wet" injection. In this regard, the aforementioned '332 patent uses a large number of axially aligned disk springs in attempting to defeat this shortcoming. However, these disk springs not only make the injector somewhat heavy, they are much more complicated and they do not necessarily output a uniform compression load. In attempting to overcome the problems associated with the disk springs as a power source, a simpler and stronger coil spring has been contemplated in place of the disk springs, as disclosed for example in U.S. Pat. No. 4,722,728 issued to Dixon. The coil spring, however, has aforementioned shortcomings in that they do not produce a substantially constant ejection pressure output.
In addition, a coil spring operated system is limited in terms of the amount of maximum force that can be exerted on the plunger for a given size thereof. Generally, it is desirable to have a more compact, user friendly device, but if a larger force is desired, the size of the coil spring has to be accordingly increased, contrary to the desirability of compactness. Moreover, for a given compact size, greater force variation is desired to allow for injection of a variety of medications and doses. The known devices do not remedy the deficiencies evident in these trade offs.
In the aforementioned '508 patent, in attempting to regulate the amount of pressure applied to the plunger of a needleless injector, a powered vacuum-compression unit is used as an energy source. While the pressure can be regulated using such a device, the portability and size are severely compromised as a separate power supply is needed to run the vacuum-compression unit.
Another energy source previously contemplated in this field is a gas propellant, such as a CO.sub.2 cartridge, as described in the aforementioned '824 and '765 patents, where the CO.sub.2 gas from the cartridge is used to propel the plunger and expel medication out of the nozzle assembly. However, the drawback with the CO.sub.2 cartridge is that it can only generate a limited pressure range and the pressure output is highly sensitive to the ambient temperature. The pressure of CO.sub.2 fluctuates with the change in the ambient temperature. In this regard, to properly operate the device, independent of the ambient temperature, it becomes necessary to include a pressure regulator device, further complicating the device.
In the aforementioned '334 patent, in attempting to generate pressure necessary to force the plunger, a gas generating pyrotechnic charge is contemplated. Specifically, the charge is detonated to produce pressurized gas acting upon the plunger. Again, this type of device has many shortcomings. First, the pressure generated from the detonating charge can be unreliable in that the charge does not necessarily produce uniform pressure each time it is detonated. For instance, different batches of detonating charges can produce different pressure levels even if a same amount of charge is used inasmuch as different charges burn at different rates. Another drawback is that since the gas acts directly on the plunger, there is a possibility of the discharged gas seeping through the seals of the plunger and into the medication and contaminating it. Even worse, there is the undesired possibility of the discharged gas being injected through the skin, especially if the pressure exceeds the operational limits.
Even pneumatic types of energy source have been contemplated, as described for example in U.S. Pat. Nos. 2,764,977 issued to Ferguson; U.S. Pat. No. 2,737,946 issued to Henin, Jr.; U.S. Pat. No. 2,322,245 and U.S. Pat. No. 2,380,534 issued to Lockhart for propelling a plunger of a needleless injector. Specifically, a pressurized chamber defined by the injector's main housing is further compressed manually to store energy, which is to propel the plunger. However, they have not been designed to deliver medication under substantially constant pressure throughout the injection period, suffering the same predicament of the coil operated devices.
It is desirable to simplify the needleless injector and the use thereof as much as possible, as well as making the same compact and light for portability. Such improvements make the device user friendly to encourage rather than discourage use of the device. In this regard, U.S. Pat. No. 4,507,113 issued to Dunlap; and U.S. Pat. Nos. 4,883,483 and 4,662,878 issued to Lindmayer describe an adapter for filling the internal chamber of a nozzle assembly from a medication supply vial directly through the ejection orifice. This not only results in essentially zero residual medication retention in the injector following the dispensing of the medication, but also eliminates any need for a complex valve arrangement or medication supply arrangement described for example in U.S. Pat. Nos. 4,059,107 issued to Iriguchi et al. and U.S. Pat. No. 3,908,651 issued to Fudge that otherwise needs to be built into the needleless injector.
The adapter described in the aforementioned '113 patent uses a bayonet mount that requires alignment and rotation. Similarly, the adapters described in the aforementioned '483 and '878 patents have a threaded mount that also has a rotary connection. Another drawback with these adapters is that a sharp hollow probe protrudes beyond the length of the main body, which if not handled carefully can injure the user, i.e., needle sticking.
It would be desirable to proliferate use of needleless injectors by providing a safe, simple disposable adapter or coupling device that can be quickly connected and disconnected to the injector. We have invented such a coupling device.
We have invented a needleless injection device that can overcome the above noted drawbacks by providing additional improvements to presently available needleless injectors. Moreover, we have invented an improved gas spring that can be used with any needleless injection device and other devices. These devices can include a projectile launching device such as an air gun. In this regard, U.S. Pat. Nos. 5,193,517; 4,771,758; and 4,709,686 all issued to Taylor et al. disclose some examples of known gas springs for use in air guns.